Process for the synchronization of ovulation for timed breeding without heat detection

ABSTRACT

A method for synchronizing ovulation in sows and gilts by a single injection of hormones is disclosed. A hormone, gonadotropin releasing hormone (GnRH), luteinizing hormone (LH), follicle stimulating hormone (FSH), human chorionic gonadotropin (hCG), analogues, derivatives, agonists or combinations thereof is administered to an open sow post weaning at a specific time to stimulate ovulation of mature responsive follicles. The sow is then bred, without heat detection, at a specific subsequent timed interval after injection with hormone, with one or two artificial or natural breedings. In gilts, the hormone is injected at a timed interval from onset of estrus or at a specific timed interval following Prostaglandin F2a for those gilts which have been held in a state of pseudopregnancy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 15/154,320, filed May 13, 2016, which is a continuation of U.S. Ser. No. 14/540,470, filed Nov. 13, 2014 (now issued U.S. Pat. No. 9,351,818), which is a continuation of U.S. Ser. No. 13/685,989, filed Nov. 27, 2012 (now issued U.S. Pat. No. 8,937,044), which is a continuation of U.S. Ser. No. 11/682,546, filed Mar. 6, 2007, which is a continuation of U.S. Ser. No. 10/954,314, filed Sep. 30, 2004 (now issued U.S. Pat. No. 7,205,281), which claims priority to U.S. Ser. No. 60/508,509 filed Oct. 3, 2003 entitled “Process for the Synchronization of Ovulation for Timed Breeding Without Heat Detection” by James W. Lauderdale, each of which are herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to the reproductive management of sows and gilts and more particularly processes for synchronizing ovulation in such swine for timed artificial breeding with a reduction in or with no regard to estrus detection.

BACKGROUND OF THE INVENTION

The administration of hormones to control the reproductive process in domestic animals such as horse, cows, sheep, goats and swine is well known in the art. One approach to managing reproductive processes in domestic mammals involves the direct administration of gonadotropines to domestic animals. Gonadotropins are produced by the anterior lobe of the pituitary gland and are characterized as follicle stimulating hormone (FSH) and luteinizing hormone (LH). Typically such hormones are extracted from the porcine pituitary glands and are administered to domestic animals to control or stimulate the ovulatory process. One gonadotropin formulation is FSH-P produced by Schering-Plough Corp. FSH-P has a fairly high and variable content of luteinizing hormone and while effective in producing an ovulatory response, has been less than desirable in producing high fertilization rates and viable embryos.

Another formulation, which contains a low and controlled level of luteinizing hormone with high follicle stimulating activity, is disclosed in U.S. Pat. No. B1 4,780,451 to Donaldson. Gonadotropin release hormone (GnRH) can also be used to stimulate ovulation as related in U.S. Pat. No. 5,180,711 to Hodgen. In that instance GnRH is administered subsequent to a GnRH antagonist which effectively suppressed natural gonadotropin levels. The GnRH then stimulates the release of endogenous FSH and LH leading to follicle development and ovulation. The use of similar hormones for control of ovulation in cattle is described in U.S. Pat. No. 5,589,457 to Wiltbank.

A number of different preparations of gonadotropins are available commercially including Fertagyl, Cystorelin, Chorulon, Folltropin-V, Factrel, PG600, Receptal and others. In addition, certain GnRH analogs, or agonists, such as deslorelin and buserelin are also available. These hormones may be administered to the various domestic species by implant, by intramuscular or subcutaneous injection or by mucosal applications such as intranasal and intravaginal routes. Gonadotropins may also be administered with excipients or delivery systems, which delay or control the release over time to produce more natural or even extended release patterns of LH. See U.S. Pat. No. 6,051,558 to Burns, et. al.

A major goal of commercial swine production is to maximize reproductive efficiency. Increased reproductive efficiency offers producers substantial opportunities to reduce production costs and enhance profitability. Part of the production costs is the result of a heavy reliance on daily heat detection of individual animals (W. L. Flowers and H.-D. Alhusen, (1992) J. Animal Science 70:615-621) since gilts and sows are bred based on spontaneous estrus cycles. Approximately half of the labor in swine breeding facilities is devoted to detection of estrus in breeding gilts and sows. Gilts or sows must be checked at least once daily in order to be bred at the correct time, and, if artificial insemination (“AI”) is used, it may be necessary to check twice daily in order to achieve the best results. Rigorous heat detection is necessary because it is difficult to predict the day of heat for any cyclic gilt or open sow, even with good heat detection records.

It is therefore an object of the present invention to provide a means of inducing ovulation that allows for artificial insemination in the absence of heat detection.

SUMMARY OF THE INVENTION

A method for synchronizing ovulation in swine in order to provide for effective reproductive management through timed artificial insemination without estrus (heat) detection has been developed. A hormone, gonadotropin releasing hormone (GnRH), luteinizing hormone (LH), follicle stimulating hormone (FSH), human chorionic gonadotropin (hCG) or a combination drug with similar activity such as PG600, is administered to a postpartum sow at a timed interval post weaning in order to stimulate ovulation. After a suitable period of time (according to breed of swine and farrowing records), a single timed AI breeding is administered to achieve normal pregnancy rates and litter sizes with no regard to estrus detection.

Preferably the GnRH is administered in the form of 50 mcg of deslorelin in an extended release carrier such as the SAIB excipient available from Birmingham Polymers. Other GnRH preparations may be administered in the range of 10-100 mcg. Such products as hCG may be administered in doses as high as 750 IU. The dose amounts as designated herein are for the hormones in their “native form” or in the case of GnRH analogs, such as deslorelin, are designated as the equivalent amount of the hormone in question in the “native form.”

Examples demonstrate that the method of synchronization was highly effective as compared to controls requiring much more labor intensive breeding techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are graphs showing that a single injection of 50 mcg of deslorelin in SAIB produced a LH peak about twice normal value (FIG. 1a ), compared to Hansel et al., (1973) Biology of Reproduction 8, 222) (FIG. 1b ), which returned to base level by 18 hours as determined by RIA.

DETAILED DESCRIPTION OF THE INVENTION

Effective reproductive management of swine has become an important factor for swine producers, particularly in view of continued vertical integration of the industry where the predominant model is an “all-in-all-out” method of production. In this method waves of pigs are produced for cost efficiencies, disease control and feed rationing to produce groups of pigs meeting ideal marketing weights at the same time. Reproductive control is the first step in the process whereby farrowing houses are filled with gilts and/or sows which are bred to farrow during a tight interval, usually 5 to 7 days. This assures that weaning of piglets from the whole farrowing house can occur on the same day and in turn groups of pigs from any one unit are of the same age, close in size and stage of development. In commercial swine husbandry this helps control disease, reduces stress among aggregated groups and maximizes the utilization of various feed formulations as the pigs proceed toward market weight.

It is well known by those skilled in the art of swine production that to maximize reproductive efficiency estrus detection becomes an important and major task. Estrus is the period of boar or breeding receptivity. Estrus detection, as presently practiced on commercial swine farms, is a daily or twice daily labor-intensive process. The process involves individual exposure of each gilt or sow to a boar and manually putting back-pressure (the “riding test”) on each animal to determine if the standing heat “immobilization” reflex is triggered (Gordon, I., Controlled Reproduction in Pigs, CAB International, 1997). This is performed on each individual in the breeding pool not known to have been recently bred and gone out of estrus. The process continues right through the estrus period and the sow or gilt is bred multiple times until it no longer is deemed receptive.

At the start of a normal estrus (heat) in domestic animals, the brain secretes large amounts of GnRH that in turn causes a release of follicle stimulating hormone and luteinizing hormone (LH) which will cause ovulation of the Graafian follicles over a 24-48 hour time period. In swine, peak estradiol levels occur several days prior to the signs of estrus and, indeed, the LH peak often occurs at the time estrus is evidenced (Niswender et al Endocrinology 37, 576-580 (1970)).

The duration of the estrus cycle in the sow is relatively constant year round at 21 days without obvious seasonality (Asdell, (1964) Patterns of Mammalian Reproduction, 2nd edn. Cornell University Press, Ithaca, USA, pp. 670; Dziuk, (1991) Reproduction in the pig. In: Cupps, P. T. (ed.) Reproduction in Domestic Animals, 4th edn. Academic Press, New York, pp. 471-489) although there may be some tendency for less consistency in late summer (Stork, M. G. (1979) Veterinary Record 104, 49-52; Hurtgen and Leman, (1980) J. Amer. Vet. Med. Ass. 177, 631-635) possibly due to shortened day length. Gilts may tend toward shorter cycles than mature sows (Asdell, (1964) Patterns of Mammalian Reproduction, 2nd edn. Cornell University Press, Ithaca, USA, 670pp.). Behavioral estrus occurs over a 2-8 day period, the onset of which is preceded by peak estradiol levels and coincides with peak LH levels (Hansel et al., (1973) Biol. Repro. 8, 222) which are responsible for the maturation and ovulation of follicles (Hunter and Polge, (1966) J. Repro. Fert. 12, 525-531; Hunter (1977) Brit. Vet. J. 133, 499-501). Ovulation occurs about 40 hours after the onset of estrus if estrus is 2 days in duration or about 75% of the way through the estrus if it is longer than 2 days (Gordon, 1997 Controlled Reproduction in Pigs, CAB International, 1997). The multiple ovulations occur over approximately 1-6 hours (Betteridge and Raeside, (1962) Res. Vet. Sci. 3, 390-398; Du Mesnil du Buisson and Signoret, 1970 Du Mesnil du Boisson, F. and Signoret, J. P. (1970) Vet. Rec. 87, 562-568; Soede and Kemp, 1993 Soede, N. M. and Kemp, B. (1993) Theriogenology 39, 1043-1053).

Attempted hormonal control of the estrus period and ovulation is well described in the literature. The controls have been described using more than one steroid/gonadotropin/prostaglandin or their analogs in series or combination of injections at various timings depending on the nature of the particular group, including pre-pubertal and pubertal gilts, sows farrowed but pre-weaning, at the time of weaning or post weaning. Injectable and oral progesterone and progestagens (Ulberg et al (1951) J. Animal Sci. 10, 665-671); Gerrits et al., (1963) J. Animal Sci. 21, 1022-1025), altrenogest (Martinat-Botte st al., 1985 Martinatt-Botte, F., Bariteau, F., Badouard, B. and Terqui, M. (1985) J. Reprod. Fert. Suppl. 33, 211-228) altrenogest with PMSG and GnRH/hCG (Busch et al., (1992) Monatehefte fur Veteriarmedizin 47, 307-316), prostaglandins (Jackson and Hutchinson, Veterinary Record 106 33-34), methallibure, PMSG and hCG (Polge et al., (1968) Veterinary Record 83, 136-142; F. De Rensis et al., (2003) Animal Reproduction Science 76: 245-250) have either met with limited success (progestagens), failed (prostaglandins), been banned from the market (methallibure) or require daily oral dosing (altrenogest), multiple injections (estradiol, progesterone) or combinations of drugs (PMSG, hCG GnRH) coupled with continued heat detection in order to create detectable breeding efficiencies.

Those skilled in the art continue to use multiple sequential hormonal intervention in order to control the time of estrus and time of ovulation in the estrous cycling gilt, such as a sequence of altrenogest or methallibure to inhibit pituitary gonadotropin followed by eCG or hCG or a GnRH, and postpartum sow, such as eCG post-weaning followed by a GnRH or a combination of a GnRH and hCG with breeding by a timed AI (Brussow et al, (1996) Theriogenology 46: 925-934). GnRH has been investigated as a “fertility enhancer” in the sow by injecting 1 day or 11 to 12 days following first service (Peters et al, (2000) Vet. Record 147:649-652). As recently as 2003 (DeRensis et al, 2003), those skilled in the art continued to investigate PG 600 injected at or prior to weaning as a method to shorten the wean to estrus interval but not for timed ovulation for timed breeding. Recent reviews of the hormonal methods to control estrus and breeding of estrous cyclic gilts and postpartum sows continue to cite processes as identified above (Kirkwood, (1999) Swine Health Prod. 7(1):29-35; Day, et al. Control of reproduction in the female pig. 30th Annual Meeting, American Association of Swine Practitioners, Workshop #6, St. Louis, Mo. Feb. 27, 1999, pp. 23-39). The scientific literature from the early 1960s through 2003 reports the requirement for either multiple sequential hormonal treatments in estrous cycling gilts or the use of various combinations of or single use of gonadotropins for attempting to manage the time of estrus in postpartum sows. No one skilled in the art has reported on a single injection of a GnRH postpartum followed by one or two timed breedings resulting in normal fertility in the absence of estrus detection and breeding associated with the detected estrus.

The ultimate goal of synchronizing estrus and/or ovulation, reducing post weaning to estrus intervals or breeding gilts as replacements is to keep the farrowing houses full and grouped for all-in-all-out production. Meanwhile, all breeding management programs utilize standard heat detection methods throughout the early detection and estrus period until breeding is complete and the gilt or sow is no longer receptive.

There is a wealth of information indicating that hormonal induction of estrus post weaning with individual gonadotropins or with a combination drug such as PG600 is efficacious in producing a fertile estrus after weaning (Kirkwood, R. N. (1999) Swine Health Prod. 7(1):29-35; Sechin et al., (1999) Theriogenology 51:1175-1182). However, F. De Rensis et al. state that while injection of gonadotropins at weaning will produce an earlier fertile estrus, by inducing an earlier estrus the time between onset of estrus and ovulation increases, making prediction of ovulation even more difficult (Knox et al. (2001) J. Animal Sci. 79:796-802). Furthermore, the research has demonstrated that the success of inducing a fertile estrus is correlated with the day of lactation when treated, with the highest success correlated to treatment on day 25 post partum (Hodson et al. 1981), which is inconsistent with those commercial programs which wean 17-21 days after farrowing. In all cases, the success of these experimental protocols was coupled with daily or twice daily estrus detection through the period of receptivity and with multiple breedings.

I. Methods for Administration

The method for synchronizing ovulation in swine without heat detection includes the steps of administering to a swine, usually at 21 days following the time of weaning, a dose of a hormone such as a gonadotropin releasing hormone (GnRH), a luteinizing hormone (LH), a human chorionic gonadotropin (hCG), derivatives or analogues thereof, or combinations thereof; in an amount effective to stimulate ovarian follicle ovulation; and after approximately one day, breeding the sow without heat detection. Breeding may be natural or artificial.

Preferably, the swine is a postpartum sow and most preferably the hormone is administered to the sow 96 hours after weaning her piglets. In another embodiment, the swine is a postpartum sow on the first day of estrus postweaning; and hormone is administered and the swine bred without further heat detection. Alternatively, the hormone is administered at the first detectable signs of estrus.

Preferably, the sow is bred about 28 hours after the hormone is administered. A second breeding may be performed.

Pubertal gilts may have hormone administered on the first day of estrus, and be bred without further heat detection. In a preferred embodiment, the hormone is administered at the first detectable sign of estrus. In still another embodiment, the gilt is in a state of pseudopregnancy and has been administered a dose of Prostaglandin F2a. In one embodiment, the GnRH hormone is administered 48 hours after Prostaglandin F2a administration. In one embodiment, the swine was pregnant and the Prostaglandin F2a was administered for the purpose of synchronized abortion. In this embodiment, the GnRH is preferably administered 48 hours after abortion is completed.

Studies have now demonstrated that a timed injection of a single hormone such as deslorelin (GnRH analog) in SAIB excipient and timed breeding with no heat detection results in normal fertility and piglet numbers in post weaned sows. The timed injection and timed breeding abruptly curtails heat detection after the first sign of estrus is detected. A timed injection of a single hormone, deslorelin (GnRH analog), in SAIB excipient and timed breeding with no heat detection can also be used following prostaglandin PGF2a administration in gilts in a state of pseudopregnancy.

II. Compositions for Synchronization of Estrus

Hormones

The composition contains gonadotropin releasing hormone (GnRH), luteinizing hormone (LH), human chorionic gonadotropin (hCG), derivatives or analogues thereof, and combinations thereof, in an amount effective to stimulate ovarian follicle ovulation; As demonstrated in the examples, deslorelin was used at a dose of 50 mcg in SAIB administered subcutaneously near the vulva. The dosages of comparable hormones in their native form or other GnRH analogs thereof have approval for some applications in meat and dairy animals. Subject to the requirements for FDA approval, and, as will be recognized by those skilled in the art, such doses may vary since there is currently no FDA approved swine label indication.

By the term “native form” is meant the hormone having the same amino acid sequence and the same activity scale as found in nature. Thus, the native form of GnRH will include the form of the hormone, regardless of how synthesized, which is as it is produced by the hypothalamus. GnRHs which are commercially available under the trademarks Cystorelin or Factrel, are synthetic products of the same amino acid sequences and activities as naturally occurring in the animal, and are therefore considered to be the native form of the hormone. The dosage rates that are given herein are for the analog of GnRH, deslorelin, and corresponding adjustments should be made for the native forms, which have lower activity. Thus the dosage of 50 mcg of deslorelin is the dose rate for an analog of the GnRH hormone so that a native form having, as one example, one-fifth the activity would have to be dosed at a rate of 250 mcg.

Excipients

In the preferred embodiment, the hormone is suspended or dissolved in an injectable excipient. In the most preferred embodiment, this is a material such as SAIB, which is obtained from Durect under the trademark SABERT™ Delivery System. This uses a high-viscosity base component, such as sucrose acetate isobutyrate (SAIB), to provide controlled release of active ingredients. After administration of a SABER™ formulation, the solvent diffuses away, leaving a viscous, adhesive matrix of the three components—SAIB, drug, and any additives. This system includes a water insoluble, high-viscosity base component, a small amount of pharmaceutically acceptable organic solvent, such as ethanol, NMP, or Miglyol® 810, to create a low-viscosity solution before application, can be administered via injection, orally, or as an aerosol, and forms an adhesive, biodegradable depot for drug delivery. These can be designed to release drug over a period of one day to three months. The more rapid delivery is desired for this application.

Other suitable excipients can also be used. BASF markets PLURONIC™ type materials, which are block copolymers based on ethylene oxide and propylene oxide. They can function as antifoaming agents, wetting agents, dispersants, thickeners, and emulsifiers. Other materials include hydrogel forming materials such as collagen, hyaluronic acid, alginate, and fibrin. Many other extended release materials and devices are also available, including various medical depo devices having similar release profiles. Other extended or sustained release formulations can be made using materials such as ion exchange resins or polymeric delivery devices.

The present invention will be further understood by reference to the following non-limiting examples.

Example 1: Treatment with a Single Dose of Hormone Yielded Higher Litter Sizes

A dose response study was performed using deslorelin in SAIB in an ovariectomized estrogen primed gilt model (Barb, et al. (1999) Proceed. Int'l. Symp. Control. Rel. Bioact. Mater., 26). As shown in FIG. 1 a, 50 mcg of deslorelin in SAIB produced a LH peak about twice normal value, compared to Hansel et al., (1973) Biology of Reproduction 8, 222) FIG. 1b , which returned to base level by 18 hours as determined by RIA.

Example 2: Comparison of Intravulvular Administration with Injection of Deslorelin

Based on these results a study was performed utilizing mature postpartum sows with 75 test individuals and 75 controls. Sows were assigned randomly in blocks of two to either control or to be injected intravulvar with 50 mcg of deslorelin in SAIB at the time of estrus detection for sows first detected in estrus in the a.m. and 12 hours later for those first detected in estrus in the p.m. Treated animals were bred AI upon detected estrus and again 24 hours later if still in estrus. Controls received a saline injection on first detected estrus behavior estrus detection and were bred according to the farm's normal procedures.

As shown in Table 1, there was no significant difference in pregnancy rates for sows of the Control versus Treated groups but there were 0.6 greater number of live piglets born per litter in the treated group versus control group.

TABLE 1 Estrus and Pregnancy Rates After Deslorelin Treatment In Sows Saline Deslorelin (Control) (Treated) Length of Estrus (Hrs.) 40.74 (n = 73) 40.81 (n = 69) Pregnancy Rate  92% (n = 75)  91% (n = 75) Saline sows bred at detected estrus consistent with farm sows. Deslorelin sows injected intravulvar with 1 ml (50 μg deslorelin acetate) at first estrus detection and AI, then AI again if in estrus the next day. Live piglet number 0.6 > in Deslorelin versus Saline sows.

Example 3: Normal Pregnancy Rates were Attained Following Hormone Treatment in Sows

Approximately 170 postpartum sows were randomly divided into two equal groups comprised of controls and treated. Following weaning, the controls were detected for estrus and bred following the normal standard operating procedures for the farms on which they resided. The treated sows received a 50 mcg dose of deslorelin in SAIB at 96 hours post-weaning and were bred with a single insemination 28+/−2 hours later with no regard to estrus detection. The sows were examined for pregnancy by ultrasound at 21 days and slaughtered around 28 days post breeding. The entire reproductive tract was removed and corpora lutea and embryos were counted.

The data in Table 2 demonstrates that normal pregnancy rates were attained following a single timed injection of deslorelin in SAIB, at a timed interval post-weaning, followed by a single timed insemination, in the absence of any estrus (heat) detection.

TABLE 2 Pregnancy Rates and Embryo Numbers After Deslorelin Treatment in Sows Number In Sows Live Embryo Pregnancy Group Pregnant Embryos CL Survival Rate Controls 82 54 13.6 20.2 68% 66% Treated 84 60 13.4 20.9 64% 71%

Example 4: Normal Litter Sizes and Pregnancy Rates were Attained Following Hormone Treatment in Sows

Postpartum sows were randomly distributed into three different groups comprised of Controls, Treatment 1, and Treatment 2, with the exception of Site 3, which was divided into two groups, Control and Treatment 2. Control sows were detected for estrus following weaning, and bred following the normal standard operating procedures for the farms on which they resided. Treatment 1 sows were detected for estrus following weaning, and received a 50 mcg dose of deslorelin in the morning when standing and were bred by AI 4 hours later and again at 24+/−2 hours later. Treatment 2 sows received a 50 mcg dose of deslorelin in SAIB at 96 or 120 hours post-weaning and were bred with a single insemination 28+/−2 hours later with no regard to estrus detection.

As shown in Table 3, Table 4, and Table 5 deslorelin treatment resulted in normal litter sizes in sows regardless of estrus detection.

TABLE 3 Litter Size After Deslorelin Treatment in Sows Site 1 Number in Avg. Total Pigs Avg. Total Live Group Born Pigs Controls 38 12.74 11.35 Treatment 1 39 12.10 11.03 Treatment 2 40 12.37 11.24

TABLE 4 Litter Size After Deslorelin Treatment in Sows Site 2 Number in Avg. Total Pigs Avg. Total Live Group Born Pigs Controls 68 11.23 10.57 Treatment 1 72 11.21 10.25 Treatment 2 66 10.88 10.02

TABLE 5 Litter Size After Deslorelin Treatment in Sows Site 3 Number in Avg. Total Pigs Avg. Total Live Group Born Pigs Controls 58 11.26 10.58 Treatment 2 60 11.09 10.27

As shown in Table 6, normal pregnancy rates were obtained following deslorelin treatment in sows.

Table 3, Table 4, and Table 5 demonstrate that normal litter sizes were attained following treatment with a single dose of deslorelin in SAIB in postpartum sows. Table 3, Table 4, and Table 5 represent data obtained from three different farm sites. Table 6 summarizes the data from Table 2, Table 3, Table 4, and Table 5, and demonstrates that normal pregnancy rates were obtained following deslorelin treatment in sows. Significantly, these results demonstrate that the same number of pigs can be obtained with the least amount of labor.

TABLE 6 Pregnancy Rate After Deslorelin Treatment in Sows Number in Number Group Pregnant % Pregnant Controls 246 172 69.92% Treatment 2 250 177 70.80%

It will be understood that modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of appended claims. 

What is claimed:
 1. A method of synchronizing time of insemination in a weaned sow, the method comprising the steps of administering to the sow a hormone selected from the group consisting of a gonadotropin releasing hormone (GnRH), or an analog thereof, without a multiple sequential hormonal intervention, wherein the hormone is administered to the sow after a timed interval post weaning of the piglets and wherein the administration of the hormone is performed without heat detection; and breeding the sow at a defined time after administration of the hormone wherein the breeding step is a single artificial insemination step.
 2. The method of claim 1 wherein the hormone is in a composition and the composition is for an intravaginal route of administration.
 3. The method of claim 1 wherein the hormone is in a composition and the composition is a low-viscosity, polymeric composition.
 4. The method of claim 1 wherein the hormone is in a kit, further comprising instructions for use, wherein the instructions for use describe steps for synchronizing the time of insemination in the sow.
 5. The method of claim 1 wherein the hormone is administered in a polymeric delivery device. 